[3.16.y-ckt stable] Patch "can: kvaser_usb: Read all messages in a bulk-in URB buffer" has been added to staging queue

Luis Henriques luis.henriques at canonical.com
Tue Mar 24 15:34:25 UTC 2015

This is a note to let you know that I have just added a patch titled

    can: kvaser_usb: Read all messages in a bulk-in URB buffer

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:


This patch is scheduled to be released in version 3.16.7-ckt9.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see



>From d5da657612af795f5e88876b42e5e5fef999383a Mon Sep 17 00:00:00 2001
From: "Ahmed S. Darwish" <ahmed.darwish at valeo.com>
Date: Thu, 26 Feb 2015 10:22:02 -0500
Subject: can: kvaser_usb: Read all messages in a bulk-in URB buffer

commit 2fec5104f9c61de4cf2205aa355101e19a81f490 upstream.

The Kvaser firmware can only read and write messages that are
not crossing the USB endpoint's wMaxPacketSize boundary. While
receiving commands from the CAN device, if the next command in
the same URB buffer crossed that max packet size boundary, the
firmware puts a zero-length placeholder command in its place
then moves the real command to the next boundary mark.

The driver did not recognize such behavior, leading to missing
a good number of rx events during a heavy rx load session.

Moreover, a tx URB context only gets freed upon receiving its
respective tx ACK event. Over time, the free tx URB contexts
pool gets depleted due to the missing ACK events. Consequently,
the netif transmission queue gets __permanently__ stopped; no
frames could be sent again except after restarting the CAN
newtwork interface.

Signed-off-by: Ahmed S. Darwish <ahmed.darwish at valeo.com>
Signed-off-by: Marc Kleine-Budde <mkl at pengutronix.de>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
 drivers/net/can/usb/kvaser_usb.c | 28 +++++++++++++++++++++++-----
 1 file changed, 23 insertions(+), 5 deletions(-)

diff --git a/drivers/net/can/usb/kvaser_usb.c b/drivers/net/can/usb/kvaser_usb.c
index fa12e7cfcc95..66b259bd9bce 100644
--- a/drivers/net/can/usb/kvaser_usb.c
+++ b/drivers/net/can/usb/kvaser_usb.c
@@ -12,6 +12,7 @@
  * Copyright (C) 2012 Olivier Sobrie <olivier at sobrie.be>

+#include <linux/kernel.h>
 #include <linux/completion.h>
 #include <linux/module.h>
 #include <linux/netdevice.h>
@@ -403,8 +404,15 @@ static int kvaser_usb_wait_msg(const struct kvaser_usb *dev, u8 id,
 		while (pos <= actual_len - MSG_HEADER_LEN) {
 			tmp = buf + pos;

-			if (!tmp->len)
-				break;
+			/* Handle messages crossing the USB endpoint max packet
+			 * size boundary. Check kvaser_usb_read_bulk_callback()
+			 * for further details.
+			 */
+			if (tmp->len == 0) {
+				pos = round_up(pos,
+					       dev->bulk_in->wMaxPacketSize);
+				continue;
+			}

 			if (pos + tmp->len > actual_len) {
@@ -982,8 +990,19 @@ static void kvaser_usb_read_bulk_callback(struct urb *urb)
 	while (pos <= urb->actual_length - MSG_HEADER_LEN) {
 		msg = urb->transfer_buffer + pos;

-		if (!msg->len)
-			break;
+		/* The Kvaser firmware can only read and write messages that
+		 * does not cross the USB's endpoint wMaxPacketSize boundary.
+		 * If a follow-up command crosses such boundary, firmware puts
+		 * a placeholder zero-length command in its place then aligns
+		 * the real command to the next max packet size.
+		 *
+		 * Handle such cases or we're going to miss a significant
+		 * number of events in case of a heavy rx load on the bus.
+		 */
+		if (msg->len == 0) {
+			pos = round_up(pos, dev->bulk_in->wMaxPacketSize);
+			continue;
+		}

 		if (pos + msg->len > urb->actual_length) {
 			dev_err(dev->udev->dev.parent, "Format error\n");
@@ -991,7 +1010,6 @@ static void kvaser_usb_read_bulk_callback(struct urb *urb)

 		kvaser_usb_handle_message(dev, msg);
 		pos += msg->len;

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